The present invention relates generally to electric and hybrid electric vehicles, and more particularly, to an improved permanent magnet motor control system for use in electric and hybrid electric vehicles.
The assignee of the present invention designs and develops electric and hybrid electric vehicles. In recent years various techniques have been published in the literature that address position sensorless operation of permanent magnet synchronous motors. Most of these techniques are based on either a fundamental component voltage model of the motor or on the spatial inductance of the salient rotor motor.
Permanent magnet synchronous motors have been considered for electric and hybrid electric vehicle applications because of their high torque to inertia ratio, superior power density and high efficiency. For high performance control applications, permanent magnet drive systems require absolute rotor position and speed signals which can be obtained from rotor position sensors such as resolvers and hall effect sensors mechanically coupled to the rotor shaft of the motor. This coupling as well as electrical connectors and signal wires from the sensor to the controller reduce mechanical robustness of the overall system. This reduction in mechanical robustness and cost of the sensors and electrical interface make elimination of these devices very desirable.
The conventional control techniques described above have limited operational range. The first technique, based on the fundamental component voltage model, cannot be used at or near zero speed operation because it requires integration of the stator voltages which are zero at stand-still and are very small near zero speed. This will cause oscillatory torque during start-up. The second technique based on the spatial information is not efficient in high speed operation because it requires high frequency injection in order to realize the absolute rotor position. This limits the available DC link voltage, which is not desirable in electric and hybrid electric vehicle applications.
It would therefore be desirable to have an improved permanent magnet motor control system for use in electric and hybrid electric vehicles, and the like.